This invention relates to a process for the repair of plastic parts using non-sagging, sandable polyurethane compositions. These compositions comprise the reaction product of a liquid polyisocyanate component, a liquid isocyanate-reactive mixture, and an inorganic filler mixture.
Various non-sagging polyurethane compositions are known in the art and described in, for example, in U.S. Pat. Nos. 4,444,976, 4,552,934, 4,698,408, 4,728,710, 4,743,672, 4,954,199, 4,994,540, 5,059,672, 5,164,473, and 5,166,303. Most of these patents disclose two-component polyurethanes basically consisting of a polyisocyanate or polyisocyanate prepolymer component, and a curative component which may be a polyol, polyamine, etc.
Adhesives and/or sealants are disclosed in, for example, U.S. Pat. Nos. 4,336,298, 4,444,976, 4,552,934, 4,698,408, 4,743,672, 4,954,199, 4,994,540, and 5,164,473. These adhesive compositions are also mostly polyurethanes.
Sag-resistant, urethane adhesives which exhibit anti-foaming properties are disclosed in, for example, U.S. Pat. No. 4,728,710. The polyurethane consists of a polyisocyanate prepolymer as the base component, and a mixture of polyols and primary/secondary aliphatic or aromatic di- or polyamines as the curative component. Various fillers, including talc, are disclosed by this patent.
Expandable non-sagging polyurethane compositions are described in, for example, U.S. Pat. No. 5,166,303. These compositions are prepared by mixing a liquid polyisocyanate with a hydroxyl group containing compound, a low molecular weight diol or triol, an organic di- or polyamine, and a small amount of water. The volume increase of the composition varies with the quantity of water in the formulation. These compositions are disclosed as suitable for the repair of irregular shaped surfaces, and cracks and voids. It is further disclosed that glass fillers can be included in applications where sanding may be necessary.
The two-component adhesives disclosed in U.S. Pat. No. 4,336,298 consist of a base component and a hardener component, and are described as being suitable for bonding fiberglass reinforced polyester (FRP) panels together. Fillers are normally added to the base component (i.e. isocyanate) to assist in controlling the viscosity. The hardener component consists of a polyester or polyether triol, a diamine, and a tin catalyst.
U.S. Pat. No. 4,444,976 also discloses sag-resistant adhesive two-component compositions. These compositions require an isocyanate prepolymer, and a low molecular weight polyol containing at least 2-5 hydroxyl groups and a secondary diamine having a molecular weight of up to about 325. This particular composition is described as having non-sagging characteristics without the use of large quantities of fillers.
The sag-resistant two-component adhesive compounds of U.S. Pat. No. 4,552,934 consist of a prepolymer component and a curative component. A mixture of a low equivalent weight active hydrogen containing material that is partially reacted with an organic polyisocyanate, and a diamine or polyamine are suitable for the curative component. The use of fillers is broadly disclosed.
U.S. Pat. No. 4,698,408 describes sag-resistant, two-component urethane adhesives having improved thermal stability. The base component is a isocyanate prepolymer and a polyepoxide resin, and the curative component is a mixture of a polyol, a di- or tri- primary or secondary amine group containing compound and various catalysts. Fillers may be included in the base component.
The sag-resistance two-component adhesive urethanes of U.S. Pat. No. 4,743,672 exhibit properties such as excellent tack and peel strength during the working time of the adhesive. These urethanes consist of a isocyanate prepolymer, and a mixture of polyols, poly(alkylene oxide) polyamines, catalysts, and optionally a bicyclic amide acetal. Talc is among the various fillers disclosed which may be added to the curative component.
Adhesive compositions suitable for the bonding of fiber-reinforced plastic materials, including SMC (sheet molding compound) are disclosed in U.S. Pat. No. 4,954,199. These adhesives comprise the reaction product of a polyol, diamines and/or triamines, an isocyanate, and a low molecular weight hydroxyl group containing compound. Abrasive fillers are not present in these compositions.
Sag-resistant, adhesive compositions are also disclosed by U.S. Pat. No. 4,994,540. These compositions are prepared by mixing and reacting a curative component of a polyol and an aromatic amine terminated polyether, and a base component of an isocyanate. Fillers are not necessary in these compositions either.
U.S. Pat. No. 5,164,473 discloses low-viscosity adhesives. These consist of an isocyanate component and a curative component consisting of a polyol and/or amine terminated polyether, diamines and/or triamine, and chain extenders and/or crosslinkers. Various fillers, including glass and talc, are disclosed.
The fact that glass fillers incorporated in polymers do improve the sandability is well known. Specifically, glass microballoons disclosed in U.S. Pat. No. 5,164,473 have been widely used because other than sandability, they also exhibit the often desirable effect of lowering the density of the polymer composition. On the other hand, due to their low density, microballoons have the tendency to swim to the surface of liquid polyurethane raw materials (polyols and isocyanates) and the resulting phase separation causes processing problems.